The invention relates, generally, to the realization of metal bridges with average span length, for example a few multiples of ten meters, but it is especially suited to the construction of provisional bridges intended for military usage or to rapid rebuilding of a destroyed bridge.
During military operations, it is often necessary to realize overpasses for rivers or valleys or to rebuild bridges rapidly, which have been, at least partially, destroyed.
Provisional constructions are entrusted to military civil engineering units. For average span lengths, with a few multiples of ten meters, provisional bridges composed of prefabricated elements are often available and can be implemented by a team of a few men. This type of bridge, called a xe2x80x98Baileyxe2x80x99 bridge in France, comprises longitudinal structural elements made of light lattice girders and transversal elements supporting a flooring. Taking into account the large number of elementary parts, implementing a Bailey bridge takes relatively long and the result is not really aesthetic, but this is irrelevant in the case of military operations.
However, military civil engineering units have been led, for quite some time, to operate in regions having suffered from war conditions, for the rebuilding of infrastructures, in particular overpasses, which have often been destroyed. Often, only the bridge deck has been cut off, whereas the abutments and the piers are still in position.
In order to restore communications rapidly, it appears interesting to use the provisional bridge elements available to the army of the country affected, but that equipment is not often provided in sufficient quantity. Moreover, the bridges that have been rebuilt in such a fashion are intended to remain in place for a long period, until complete rebuilding of the civil engineering works and it is not superfluous to cater for their external aspect as far as possible.
Besides, xe2x80x98Baileyxe2x80x99-type bridges were designed to be implemented manually by a few men. Still, the civil engineering units are, at the moment, fitted with lifting means whose capacity may generally be 4 or 5 tons, and it is therefore interesting to change the design of the provisional bridges while taking the current possibilities into account.
The invention therefore relates to a new bridge deck that, like dismountable bridges known previously, is composed of prefabricated elements assembled on site, but whose installation, using lifting devices, can be particularly fast, whereas such a deck may have, moreover, a longer span length than the provisional bridges known so far.
Furthermore, the bridge deck according to the invention exhibits an external aspect similar to that of a bridge built in a conventional fashion. A provisional bridge according to the invention may thus be easily turned into permanent civil engineering works.
Besides, thanks to its multiple advantages, the invention is not limited to the realization of provisional bridges, but can also be applied advantageously to the realization of any overpass with average span length.
The invention relates therefore, generally, to the realization of a deck for a metal bridge whereby at least one span rests on two supports, the deck comprising at least two main girders parallel to the longitudinal direction of the bridge and connected by a plurality of transversal spacers at a distance from one another and a transversal flooring resting on the longitudinal main girders.
According to the invention, each longitudinal girder is built by butt-jointing of a number of prefabricated metal elements, each formed of a tubular hollow coffer with polygonal transversal section with at least one plane upper face, whereas the coffers exhibit the same section and each extending over a length compatible with the transport and lifting means. Moreover, the coffers of two adjacent girders are connected in twos by a plurality of spacers, each composed of a metal tube with two ends each fitted with fastening means with one lateral face of a coffer and the girders are connected, at their upper part, by a plurality of rigid transversal junction elements making up at least a portion of the flooring and with two ends fastened respectively to the upper plane faces of the coffers of both girders.
Advantageously, each coffer forming an element of a longitudinal girder exhibits a quadrangular and, preferably trapezoid, transversal section, with two horizontal faces of different widths and two lateral faces tilted symmetrically with respect to a vertical middle plane of the coffer.
In a first embodiment of the invention, the transversal junction elements are composed of a series of profiles spaced apart from one another and extending transversally over a length at least equal to the distance between two girders, whereas the profiles have each two ends fastened respectively on the plane upper faces of the corresponding coffers of both girders.
Preferably, the junction profiles are spaced apart by a constant distance corresponding to the width of a timber span placed between two neighboring profiles and resting on the upper plane faces of the corresponding coffers of both longitudinal girders, whereas a provisional flooring is composed of a series of spans placed beside one another.
According to another advantageous characteristic, the bridge deck comprises a series of undulated panels extending between two longitudinal girders and resting on the upper faces of the corresponding coffers of the girders, whereby the panels abut one another and compose formwork for casting a concrete slab to build the flooring of the bridge deck.
In cases where the provisional flooring is composed of spans placed between junction profiles, it is possible, after removing the spans, to place between both girders, a series of undulated panels nesting over the profiles and making up formwork for the casting of a concrete slab to build the permanent flooring of the bridge deck.
Advantageously, the upper plane face of each coffer is fitted with parts protruding upwards, forming connectors, intended to be embedded in the concrete slab cast in the formwork, for interlocking the slab with the longitudinal girders.
According to another embodiment of the invention, the transversal junction elements are composed of a series of concrete slab elements intended to be butt-mounted, one after another, over at least two series of coffers forming at least two longitudinal girders, while covering the girders, whereas each element of the slab is interlocked, after assembly with the corresponding coffers of both girders, in order to build the flooring of the bridge deck.
The invention also covers a number of advantageous characteristics that will be described in more detail below and that are subject to the claims.
Besides, the invention also covers the prefabricated elements for the construction of a bridge deck and a new method for building a span that comprises such a bridge deck.
But the invention will be described better with the following description of certain embodiments particularly advantageous that are explained for exemplification and non-exhaustive purposes and represented on the appended drawings.